Eccentricity error of air-core coil is of great importance to the stability and safety of smart substations, as well as the reliable metering of electrical energy. Previous research has been mostly conducted on air-core coil with even turns. On the contrary, few studies have been done on air-core coil with uneven turns. This paper modeled the eccentricity error of air-core coil with even turns and uneven turns, respectively. The relationships between the mutual inductance and off-center distance, inhomogeneity, relative position, geometrical parameters were examined. The simulation results show that the eccentricity error will not be influenced by the inhomogeneity when the current-carrying conductor is centered. However, the error will be up to 10% under the condition of 0.5° inhomogeneity and off-center distance of one quarter of coil inner radius. The experiments on the accuracy of three designed air-core coils with respect to off-center distance was carried out. The experimental results show that when the off-center distance is less than 4 mm, the ratio error will be less than 0.2%。 And when the distance reaches 16 mm, the error will exceed 1%. to 32 mm. On the other hand, the phase difference remains almost unchanged during the experiments.